One-dimensional modelling of pile jacking installation based on CPT tests in sand

The load-transfer (t–z or q–z) curve method has been widely used for prediction of the load–settlement relationship of piles subject to axial loads because of its simplicity and good convergence. However, few studies have focused on the pile installation and friction fatigue. With this consideration, the present study develops a large-displacement t–z curve which describes the degradation of shaft friction as a function of accumulated displacement. A one-dimensional numerical analysis technique using a q–z spring and a series of t–z soil springs is proposed for simulation of the jacking installation process of a large-displacement pile. The q–z curve and the parameters of the t–z curve can be obtained by cone penetration tests. The t–z spring of each soil layer can be broken away from the lower pile node beyond the layer range and reconnected to the upper pile node with the displacement of the springs accumulated continuously. Two case studies are presented to validate the applicability of the jacked pile model. Results show that the developed model can satisfactorily simulate the axial load and shaft friction of the pile during jacked installation. It can be concluded that the amount of cyclic displacement resulting from the unloading has a significant effect on the installation resistance, which is ignored by the existing design method.